Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/36—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
  • C04B38/06—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances
  • C04B38/0615—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by burning-out added substances by burning natural expanding materials or by sublimating or melting out added substances the burned-out substance being a monolitic element having approximately the same dimensions as the final article, e.g. a porous polyurethane sheet or a prepreg obtained by bonding together resin particles
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/36—After-treatment
  • C08J9/40—Impregnation
  • C08J9/42—Impregnation with macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00793—Uses not provided for elsewhere in C04B2111/00 as filters or diaphragms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2101/00—Manufacture of cellular products
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2375/00—Characterised by the use of polyureas or polyurethanes; Derivatives of such polymers
  • C08J2375/04—Polyurethanes

Definitions

• the present invention relates to a method of increasing the cell volume of open-celled polyurethane foams and to applications of the foams so produced.
• Polyurethanes (often abbreviated to PU or PUR, hereinafter abbreviated to PUR) are obtainable by polyaddition of dihydric or higher alcohols (e.g., polyester and / or polyether diols) and isocyanates. Depending on the choice and stoichiometric ratio of the starting materials, polyadducts with different property profiles, e.g. in terms of density and hardness. With bis-functional alcohols and isocyanates, linear, thermoplastic products are obtained, polyfunctional starting materials (for example trihydric alcohols) react to form branched or crosslinked polyadducts. Polyurethanes with polyesters or polyether diols as diol component are often referred to as polyester or polyether polyurethane.
• the polyaddition is carried out in the presence of water or carboxylic acids, because they react with the isocyanates with elimination of buoyant CO 2 .
• possibly volatile substances such as fluorine-chlorine hydrocarbons (CFCs) or methylene chloride are added as blowing agent.
• CFCs fluorine-chlorine hydrocarbons
• methylene chloride methylene chloride
• a further development of the foaming technology that overcomes this problem is the use of liquid carbonic acid as an alternative blowing agent.
• a second, technically very complex alternative is foaming under constant atmospheric conditions in a closed system. At low pressure, in particular foams with low density can be produced without added blowing agent.
• PU foams as materials is that the cell structure ensures softness, elasticity and dimensional stability while maintaining low weight.
• Polyurethane foams are used in a variety of fields due to the wide range of their product properties. Main applications are upholstered furniture, cushions, mattresses, vehicle seats, car body parts, housings and packaging, insulation and Soundproofing and filters.
• polyether polyester Bulk density [kg / m 3 ] 20 - 110 20 - 60 Compression hardness [kPa] 1,5 - 20 2 - 7 (50)
• pores per inch pores per inch
• the range of variation of commercially available PUR foams ranges from fine-pored foams with more than 100 ppi to relatively coarsely porous foams with about 8 to 10 ppi.
• Open-cell foam structures can be produced by subsequently destroying the cell walls (so-called reticulation).
• the action of the shock wave of an explosion such as a blast gas explosion, the cell walls are torn open, and a characteristic framework of webs with mostly triangular web cross-section remains.
• Open-celled polyurethane foam can be used as a starting material for the production of open-cell metal or ceramic foams.
• the production of foamed ceramics comprises in a known manner the basic steps of providing a pre-structure, for example in the geometry of a later component made of an open-cell polymer foam, coating the cell webs of the pre-structure with a suspension (slurry) of ceramic or / and particles forming under high-temperature treatment Addition of excipients such as sintering additives, thickeners and / or condensers in water or other solvent, pressing and drying of the coated polymer foam, curing of the coating, burning out or pyrolysis of the polymer material and sintering of the remaining ceramic coating.
• a suspension slurry
• excipients such as sintering additives, thickeners and / or condensers in water or other solvent
• pressing and drying of the coated polymer foam curing of the coating, burning out or pyrolysis of the polymer material and sintering of the remaining ceramic coating.
• Such an industrially used method is known from US 3 090 094.
• a solution to this problem according to EP 0 907 621 is that during or after the sintering, the ceramic foam is impregnated with a melt or suspension and then heated to a temperature above the melting temperature of the substances contained in the suspension or their reaction products. As a result, the cavities are filled in the ceramic webs and possibly formed cracks and pores are closed.
• the melts or the solids of the suspension consist of materials which melt below the melting temperature of the foamed ceramic, have a similar coefficient of expansion as the foamed ceramic, wet them very well and do not react with constituents of the foamed ceramic.
• the cavities can be filled and cracks closed. Due to their permeability and high-temperature resistance, open-cell foam ceramics based on silicon carbide are suitable, among other things, for the production of burner elements in surface radiation, volume and porous burners.
• polyurethane foams with an approximately homogeneous pore distribution can only be produced up to a pore size of about 8 to 10 ppi.
• the structures collapse under the influence of their own weight.
• filters could be made more open and thus the throughput increased.
• pore burners with a ceramic foam in the flame zone a pore enlargement within certain limits causes a lowering of the temperature of the ceramic foam and a faster homogenization of the temperature distribution in unsteady processes, such as start-up or load changes.
• the key criterion for flame formation is that the Peclet number exceeds a critical value of 65.
• S L [m / s] is the laminar burning rate
• d m [m] is the equivalent pore diameter
• cp [J / kg * K] is the specific heat capacity of the gas mixture
• ⁇ f [kg / m 3 ] is the density of the gas mixture
• ⁇ f [W / m * K] is the thermal conductivity of the gas mixture.
• the invention is therefore based on the object to provide a method which allows to increase the pore volume of each pore and thus the entire structure, without reducing the stability of the foam structure so far that it collapses and collapses ,
• liquid or common solvents preferably water
• readily soluble compounds containing an aromatic skeleton eg a phenyl ring (benzene ring) and at least one hydroxy group, in particular dissociable hydroxy groups.
• aromatic skeleton eg a phenyl ring (benzene ring)
• hydroxy group in particular dissociable hydroxy groups.
• the simplest member of this group of compounds is phenol (hydroxybenzene).
• Whose use for the process according to the invention is in principle possible, but not desirable due to the toxicity of this substance. Therefore, according to the invention, preference is given to using less volatile and less harmful substances which have the above-mentioned structural feature.
• Phenolic resins are formed by condensation of phenols and aldehydes.
• the aldehyde component used is almost exclusively formaldehyde, as phenol component in addition to phenol itself also aryl- or alkyl-substituted phenols (eg, xylenols, cresols) or polyhydric phenols (eg resorcinol, bisphenol A).
• the structure of the condensation products depends on the molar ratio of the reactants and the catalysts used. Phenol excess and acid catalysis lead to the formation of compounds in which hydroxy-bearing phenyl rings are linked together via methylene groups.
• novolaks are soluble, fusible and non-self-hardening, but can be cured by the addition of another formaldehyde-releasing curing agent, eg, hexamethylenetetramine.
• another formaldehyde-releasing curing agent eg, hexamethylenetetramine.
• formaldehyde surplus and basic catalysis products are obtained in which phenyl rings carrying hydroxyl groups are at least partially connected to one another via methyl ether bridges instead of methyl groups, and the phenyl rings are in some cases additionally substituted by hydroxymethyl groups. Due to the reactivity of the methyl ether groups and the hydroxymethyl groups, these compounds are self-curing in contrast to novolaks and therefore have a limited shelf life in the liquid or dissolved state.
• Benzyl alcohol phenylmethanol
• Benzyl alcohol is classified as harmful in contrast to phenol. Since benzyl alcohol is in the liquid state at room temperature, it can be used directly in undiluted form.
• the pore-widening substances can be used either undiluted in liquid form or, for example, as aqueous or alcoholic solutions or as solutions in mixtures of water and an alcoholic solvent.
• the use of water as a solvent is preferred for cost and disposal reasons.
• the foam structure bodies of PUR which have been prepared in a known manner and converted into open-cell foams, are aged for several minutes to hours in the treatment solution. As a result of this treatment, which can be assisted by elevated temperature, application of negative pressure or application of a tension to the foam structure, the dimensions (length, width and height) of the foam structure bodies increase depending on the duration of the treatment and the concentration of the used solution by 10 to 50% in each spatial direction.
• foams having an average pore number of, for example, 10 ppi are used as the starting material, foams with an average pore number of about 6.5 ppi can be produced therefrom using the process according to the invention.
• foam structures having an average pore count of 8 ppi (upper limit according to the current state of the art) as starting material pore numbers of 5.5 to 5 ppi can be produced with the process according to the invention, which have hitherto not been commercially available.
• An important field of application of the PUR foams produced by the process according to the invention is the production of metal and ceramic foams.
• the particles with which the foam structure is to be coated are dispersed in the liquid pore-expanding substance or the solution of the pore-expanding substance.
• the further process steps follow the processes known from the prior art, for example US Pat. No.
• 3,090,094 or EP 0 907 621 and essentially comprise the basic steps of pressing out and drying the coated polymer foam, curing the coating and burning out or pyrolysis of the polymer material and sintering and if necessary Gas or liquid phases infiltrate the remaining ceramic coating.
• PUR foams having an average pore number of less than 8 ppi and ceramics or metal foams having an average pore number of less than 8 ppi produced therefrom by the process according to the invention can be used, for example, as filters.
• Ceramic foam structures of less than 8 ppi produced from the PUR foams treated by the process according to the invention are particularly suitable as flame zone structures for the combustion chambers of pore burners.
• Such burners are known, for example, from patents EP 0 657 011 and EP 1 212 258.
• the combustion chamber is a porous material with contiguous cavities, the pore size in the flow direction of the gas / air mixture from the inlet to the outlet continuously, ie within a transition zone, or discontinuously, ie at an interface increases, so that in the transition zone or at the interface exceeds the critical Peclet number for the flame development. While the flame development is suppressed in the direction of flow before the interface or into the transition zone, a flame can build up after the interface or transition zone.
• the ceramic foam with the enlarged pores according to the invention is used for the region above the critical Peclet number, ie in the actual firing zone, this area is better traversed by the combustion gases and the heat produced during combustion is better dissipated. The foam stays cooler for the same fire performance, which extends its life.
• the time is reduced to the formation of a uniformly distributed flame, which typically pulls back into the foam structure at pore burners when reaching the stationary combustion state.
• Crucial for flame formation is a Peclet number of more than 65. Because of the direct dependence of the Peclet number on the pore size (equation (1)), therefore, the pore size must exceed a critical minimum value for flame formation. The fewer pores are above this limit, the less potential areas (pores) in the foam are at which a first flame formation can take place. Typically, the other flames emanate from these "germination zones" and spread to the entire foam. With an increasing number of pores above the critical limit, there are therefore more nucleation zones for flame formation.
• the foam heats up more uniformly, more homogeneously and thus faster.
• Samples of PUR foam having a mean pore number of 10 ppi were swapped at room temperature in aqueous solutions of phenol.
• the dimensions of the samples (length x width) were 20 mm x 20 mm.
• Three parallel samples were outsourced in a solution containing 0.5% by weight of phenol and three further samples in a solution containing 5% by weight of phenol. The samples were completely immersed in the respective solutions. After a storage time of 2 and 24 hours, the length and width and the number of pores of the samples were determined. The results are shown in Table 1. The percentage length changes are always related to the length in the initial state, ie before the removal. Table 1: Results of the aging experiments in aqueous solutions of phenol Massebez.
• Phenol content of the solution 0.5% 5% Duration of test / hour. 0 2 24 0 2 24 Sample No. 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Length / mm 20 20 20 23 23 22 23 24 24 20 20 33 32 33 31 29 29 Length change /% - - - 15 15 10 15 20 20 - - - 65 60 65 55 45 45 Pore count / PPI 10 10 10 9 9 9 9 8th 8th 10 10 10 6 6 6 6 7 7
• Samples of PUR foam having an average pore number of 8 ppi were aged for 24 hours at room temperature in various concentrated solutions of a commercially available resol type phenol resin and then dried in a drying oven at 40 ° C for two hours. During the aging process, the samples were completely covered by the solution. Before and after aging, after drying and after a further two days aging at room temperature, sample length and average pore number were determined. The results are summarized in Table 2. The percentage length changes are always related to the length in the initial state, ie before the removal. Experiments were carried out with three different concentrations of the phenolic resin solution. For each experiment, another foam sample was used. The lower resin solutions were obtained by diluting the 100% resin solution with ethanol.
• Table 2 Results of the aging experiments in solutions of phenolic resin Phenol resin content of the solution 100% 50% / 50% ethanol 33.3% / 66.7% ethanol Duration of test / hour. 0 24 Drying 2 hours, 40 ° C 0 24 Drying 2 hours, 40 ° C 0 24 Drying 2 hours, 40 ° C Length / mm 65 80 80 75 90 90 70 85 85 Elongation /% - 23 23 - 20 20 - 21 21 Pore count / PPI 8th 6.5 6.5 8th 6.7 6.7 8th 6.6 6.6 6.6
• wetting properties of the phenolic-resin-coated polyurethane foam could be positively influenced, so that the slurry of ceramic-forming or / and ceramic particles applied in the subsequent step could be applied at a higher application rate (mass of applied particles per foam surface) ,
• silicon carbide powder was added to the ethanolic solutions of phenolic resin described in Example 3, so that a slip was obtained.
• PUR foam structures were paged with an average pore number of 8 and 10 ppi, respectively.
• Decisive for the quality of the coating in this variant is that the removal time is extended long enough so that after paging the pore widening is completely completed. If the coated foam structures are removed too early from the slurry, then the pore widening process continues, and cracks are formed in the coating due to the associated increase in volume. From the silicon carbide-coated foams thus obtained, silicon carbide foams were prepared as shown in Example 3.
• the ceramic foams of Examples 3 and 4 were tested for their suitability as a flame zone structure in pore burners.
• the burner comprised in the flow direction a premixing chamber, a perforated plate made of a fibrous material which formed the zone of subcritical Peclet number, and subsequently a foam structure produced by the process according to the invention, which formed the flame zone.
• the burner was fed with methane-air mixtures.
• the start-up phase of the burner (time to retract the flame into the foam) lasted about 5 to 10 seconds.
• uniform annealing was achieved in the flame zone within 12 to 15 seconds. In conventional foams with a smaller pore size, a longer time is required for this, which is usually about 20 to 30 seconds or more.
• the burners were operated for 240 seconds at a maximum power of 30 kW. This test was performed with different air ratios between 1 and 1.3. Subsequently, the power was throttled to 15 kW and increases the air ratio to 1.4, and turned off the gas supply in this operating condition, but maintained the air supply for cooling. In all experiments, the foams retained their mechanical strength and showed no visible shape changes. Conventional foams with smaller pores showed in comparative experiments a much lower stability to the thermal load, which is z. B. made by cracks, potholes or oxidation effects noticeable. In addition, a stronger heat radiation could be observed in the foams of the invention.

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• 2004
  • 2004-09-29 DE DE502004008587T patent/DE502004008587D1/de active Active
  • 2004-09-29 ES ES04023181T patent/ES2319766T3/es active Active
  • 2004-09-29 AT AT04023181T patent/ATE416224T1/de not_active IP Right Cessation
  • 2004-09-29 EP EP04023181A patent/EP1642927B1/fr not_active Not-in-force
• 2005
  • 2005-09-28 CA CA002521454A patent/CA2521454A1/fr not_active Abandoned
  • 2005-09-29 US US11/238,479 patent/US20070232707A1/en not_active Abandoned

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